The present invention relates to products made out of recycled thermoplastic material, and to a method of manufacturing them.
With ecology playing an increasing part in present-day society, industry and consumers are having to take control of the impact of their activity and their behavior on the environment in order to avoid polluting and degrading it.
One of the main problems associated with this preoccupation lies in the increasing amount of thermoplastic material used in making consumer products, and consequently lies in eliminating waste containing such materials. These materials are not rapidly biodegradable so merely dumping such waste is not a solution that is satisfactory from an ecological point of view.
To eliminate such waste, incineration has been resorted to, which achieves physical elimination of the waste and avoids the need to store it. However incineration produces flue gases that heat and pollute the atmosphere.
Another solution to the problem is recycling the products. The suitability of thermoplastic materials for recycling depends in particular on the physico-chemical characteristics thereof. Thermoplastic materials that are suitable for recycling are generally ground up and cleaned for use in the manufacturing cycle of a wide variety of novel products by being incorporated in the material from which such products are made. Thermoplastic materials that are not very suitable for recycling are generally merely ground up so as to be used as filler or packing material, or they are possibly incorporated in materials that are to constitute products of mediocre quality presenting poor mechanical characteristics.
New polyethylene terephthlate is a material that is frequently used to manufacture mass-produced products such as bottles or common consumer articles. Recycled polyethylene terephthlate, in particular when it comes from household waste, is often heterogeneous in nature having physico-chemical characteristics of relatively poor level, thereby restricting its use to manufacturing products that are thin and of mediocre quality, and that are made out of materials incorporating only a small quantity thereof. Given the volumes of products made out of new polyethylene terephthlate and the difficulty in recycling this material, recycling all of the polyethylene terephthlate that is produced is not a practical possibility at present. This is amplified by the fact that recycled polyethylene terephthlate, and indeed ordinary quality new polyethylene terephthlate, is unsuitable for use in making bulky parts that are solid. As a result the quantity of polyethylene terephthlate that can be recycled in products is limited.
It would therefore be advantageous to be able to obtain said bulky parts that incorporate recycled polyethylene terephthalate while also having good mechanical characteristics.
To this end, the invention provides a thermoplastic material part wherein the material comprises:
recycled polyethylene terephthalate;
recycled high density polyethylene;
a compatibility agent; and
a reinforcing filler, the material advantageously comprising, by weight:
approximately 49% to 63.5% and preferably 55% of polyethylene terephthalate;
approximately 27% to 36% and preferably 33% of high density polyethylene;
approximately 4% to 6% and preferably 5% compatibility agent; and
approximately 5% to 10% and preferably 7% of reinforcing filler.
This provides a part which can be solid and bulky in structure. The part also presents mechanical characteristics which are satisfactory, and in the preferred composition come close to those of wood, with this applying in particular to breaking strength, thereby enabling the part to be assembled in similar ways to wood.
The invention also provides a method of fabricating a part of the above type in the form of a bar, the method comprising the steps of:
drying flakes of recycled polyethylene terephthalate;
introducing said dried flakes of polyethylene terephthalate, flakes of recycled high density polyethylene, the compatibility agent, and the reinforcing filler into an extruder in order to obtain a paste mixture; and
introducing the paste mixture into a mold placed directly at the outlet from the extruder.
Drying the polyethylene terephthalate flakes serves to avoid hydrolysis of the polyethylene terephthalate during extrusion. It has been found that such hydrolysis gives rise directly to a reduction in the impact strength of polyethylene terephthalate.
Advantageously, the method includes a subsequent step of cooling the mixture contained in the mold.
By cooling the mixture contained in the mold immediately after the paste mixture has penetrated into the mold makes it possible to obtain a bar which has a surface layer that is in an amorphous phase which is more flexible. This improves the mechanical properties of the material, and in particular its impact strength.
The invention also provides a goods pallet comprising parallel support elements having end portions that are fixed by assembly means to cross-connection elements resting on brackets, with at least one of said elements being constituted by a beam presenting one of the above-specified characteristics.
A pallet constructed in this way can be made by assembling together various elements, and it presents properties of the same order as those of conventional pallets, and in particular wooden pallets, or indeed properties that are better than those of pallets made out of injected thermoplastic material of ordinary type.
Advantageously, at least one of the cross elements is constituted by a beam of channel section having a top flange on which the support elements are fixed, and a web and a bottom flange cut out by at least one notch to form on either side thereof two spaced-apart brackets integral with the cross element. The channel section of the beam provides good distribution of the weight supported by the pallet, thereby increasing the strength of the pallet. Furthermore, by using such a beam, the various portions of a conventional assembly are formed integrally, thus making it possible to reduce the number of parts and to simplify manufacture of the pallet.
In a particular embodiment, the pallet includes at least one stiffener element extending parallel to the support element and at a distance therefrom between two opposite brackets, the stiffener element being formed by a plank-shaped beam, the bottom surface of said beam being grooved and the beam having at least one chamfer formed on at least one of its top longitudinal edges. This makes for a pallet that is particularly strong. This also makes it possible firstly to lighten the pallet and secondly to reduce the risk of an impact between the stiffener element and the ends of lifting tines.